This application claims the benefits of Japanese Application Nos. 10-163276, 11-046551 and 11-085415 which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an elastic shaft joint which is assembled into a universal joint for constituting, for example, a steering apparatus for a car so as to transmit a motion of a steering wheel to a steering gear and to prevent a vibration on the side of the steering gear from being transmitted to the steering wheel.
2. Related Background Art
A steering apparatus for a car is arranged to transmit a motion of a steering shaft which is rotated by a steering wheel to a steering gear so as to give a steering angle to the wheels. Normally, the steering shaft and the input shaft of the steering gear can not be disposed on the same straight line. For this reason, a universal joint is arranged between the steering shaft and the input shaft to transmit a motion of the steering wheel to the steering gear. A vibration absorbing ability is conventionally given to the universal joint, in order to prevent the vibration which is transmitted from the wheels to the steering gear when the car is run from further being transmitted to the steering wheel to give unpleasant feeling to the driver. In order to give the vibration absorbing capability to the universal joint in this manner, an elastic material such as rubber is usually assembled into this universal joint so that the transmission of the vibration is prevented by use of the elastic material.
As such an elastic shaft joint or a universal joint assembling such elastic shaft joint therein, there are conventionally known joints disclosed in Japanese Patent Application Laid-Open Nos. 56-39325 (French Patent Application Laid-Open No. 2464404), 56-131831, 60-184716 to 60-184718, 60-215122, and 60-215123, 61-201924, Japanese Utility Model Application Laid-Open Nos. 54-82257, 5-83462, and 5-89964, French Patent Application Laid-Open No. 2614985, U.S. Pat. No. 4,509,775; etc.
In the elastic shaft joint conventionally known, leaving the case in which a vibration in the direction of rotation of the shaft such as a steering shaft is applied, when a vibration in the axial direction of this shaft is applied, the capacity of the shaft joint to attenuate this vibration is poor, so that the vibration in the axial direction is easily transmitted to the steering wheel. Especially, when a displacement along the axial direction is applied to a part with a shaft mounted thereon, for example, when the distance between the steering gear and the front end portion of the steering shaft is changed due to a vibration upon running of the car, this displacement can not be absorbed. Also, if it is required to absorb an tolerance in manufacturing or assembling the parts when the elastic shaft joint is to be assembled into a steering apparatus of the car, such requirement can not be satisfied. Further, when one end portion of the shaft with the elastic shaft joint assembled therein is inserted in the base end portion of a yoke of a universal joint in the axial direction thereof, this end portion of the shaft is required to be displaced in the axial direction, which also can not be satisfied.
Taking these circumstances into account, such a structure as disclosed in, for example, Japanese Patent Application Laid-Open No. 11-048991 is contrived in which a shaft is divided into a pair of elements and the paired elements are brought into serration engagement with each other at a coupling portion thereof. Since the portion of the serration engagement between the paired elements allows a large displacement in the axial direction, even when a displacement in the axial direction is applied onto a portion with the shaft mounted thereon upon running of the car, this displacement is absorbed. If an tolerance in manufacturing or assembling of the parts is required to be absorbed when the elastic shaft joint is to be assembled into the steering apparatus of the car, it is possible to prevent such tolerance. Further, when one end portion of the shaft with the elastic shaft joint mounted thereon is to be inserted into the base end portion of the yoke of the universal joint in the axial direction, it is possible to displace this end portion of the shaft in the axial direction.
However, the cost is inevitably increased when the serration engagement portion is provided in a part of the shaft. That is, in order to prevent a backlash of the serration engagement portion, irrespective of presence or absence of vibration in running, it is required to form a slit on the side of an outer shaft on which a highly accurate processing is performed or a female serration is formed, for elastically expanding or contracting the diameter of this outer shaft. Further, it is required to provide a weight member for elastically contracting the diameter of the outer shaft.
Taking these circumstances into consideration, an object of the present invention is to provide a practical elastic shaft joint which is capable of absorbing a displacement in the axial direction and securing a sufficient durability though manufactured comparatively at a low cost.
The elastic shaft joint of the present invention is to couple an end portion of a rotatable shaft such as a steering shaft and a rotary member which rotates upon rotation of such shaft, such as a yoke for constituting a universal joint, so as to absorb a certain displacement in the axial direction of the direction of rotation.
Out of such elastic shaft joints of the present invention, an elastic shaft joint according to a first aspect of the invention has a pair of outer-diameter side engagement surfaces which are substantially parallel to each other at two positions on the opposite sides of the outer peripheral surface in the radial direction. The rotary member is provided with a pair of restraint plate portions which are substantially parallel to each other and is formed to have an opening on a lateral side thereof. Then, a vibration absorbing member is provided between the rotary member and the shaft. Then, this vibration absorbing member is constituted by an elastic member which is disposed on the inner peripheral surface of a part fixed to the rotary member and a sliding sleeve which is supported by the inner peripheral surface of this elastic member, which inner peripheral surface is brought into slidable contacted with the outer peripheral surface of the shaft.
An elastic shaft joint according to a second aspect of the present invention is provided with a coupling sleeve around one end of the shaft, to allow free displacement of this shaft in the axial direction and to freely absorb a vibration to be transmitted to or from this shaft. Of the rotary member, the base portion, to which an end portion of the shaft is to be coupled and fixed, is formed to have an opening on the lateral side thereof. Then, this coupling sleeve is coupled and fixed to this rotary member to form the elastic shaft joint by inserting the coupling sleeve into this base portion from the lateral opening so as to suppress the coupling sleeve by means of this base portion.
Further, an elastic shaft joint according to a third aspect of the present invention is provided with a pair of outer-diameter side engagement surfaces which are substantially parallel to each other at two positions on the opposite sides of the outer peripheral surface in the radial direction of at least one end portion of the shaft.
A coupling sleeve is disposed in the vicinity of an end portion of the shaft. Then, rotation limiting cylinders are provided at two positions on the inner peripheral surface on the opposite sides in the radial direction, in a half part of this coupling sleeve in the axial direction which is a part closer to the end portion of this shaft. Each of these rotation limiting cylinders is provided with inner-diameter side engagement surfaces which are substantially parallel to each other and face the above-mentioned outer-diameter side engagement surfaces with a gap therebetween in a neutral state in which no phase shift is generated with respect to the direction of rotation between the shaft and the coupling sleeve, so as to limit an amount of rotation of the shaft within the coupling sleeve. On the other hand, a retaining cylinder having a larger diameter than that of the rotation limiting cylinder is provided in the other half part of the coupling sleeve in the axial direction, which is a part closer to a middle portion of this shaft. Between the inner peripheral surface of this retaining cylinder and the outer peripheral surface of the end portion of the shaft, there is provided a vibration absorbing member which prevents the transmission of a vibration to and from the coupling sleeve in the above-mentioned neutral state, but allows displacement of the shaft in the axial direction with respect to this coupling sleeve.
Further, out of the rotary member, the base portion to which one end portion of the shaft is to be coupled and fixed is provided with a pair of restraint plate portions which are substantially parallel to each other and is formed to have an opening on the lateral side thereof. Then, in a state in which the rotation limiting cylinder out of the coupling sleeve is inserted between these two restraint plate portions from the lateral opening, parts closer to the opening ends of these restraint plate portions are coupled to each other by means of a bolt so as to suppress the both restraint plate portions toward each other, thereby connecting and fixing the coupling sleeve to the rotary member.
More preferably, one or more of the following structures (1) to (4) are added.
(1) An shock absorbing member for absorbing an energy of an impact, when the impact is applied in the axial direction, is provided in series with respect to the above-mentioned shaft, to contract the total length of the shaft.
(2) A stopper is disposed between the rotation limiting cylinder and the shaft for restricting a displacement in the axial direction of the rotation limiting cylinder and the shaft within a predetermined range to prevent the shaft from being drawn out of the shaft.
(3) Sealing members for preventing foreign substances from advancing into the coupling sleeve are provided between the opening end portions of the retaining cylinder and the outer peripheral surface of the middle portion of the shaft and at the opening end portion of the rotation limiting cylinder.
(4) Locking portions are provided on the lateral portions of the paired restraint plate portions for constituting the base portion of the rotary member, while the coupling sleeve is provided with an insertion plate which can freely advance to parts opposite to these locking portions and, after the advancement, is prevented from coming off from these parts opposites to the locking portions on the basis of an engagement with these locking portions, and an elastic stretching piece which is protruded from the opening side of the pair of restraint plate portions out of the peripheral surface of the coupling sleeve, so that the coupling sleeve can be freely pressed to the interior part of the base portion on the basis of the engagement between the outer peripheral surface of the middle portion of the coupling member, which couples the rotary member to the coupling sleeve by reducing a distance between the paired restraint plate portions.
The effect obtained when a rotating force is transmitted by preventing transmission of a vibration by means of the elastic shaft joint according to the second aspect of the invention, out of the elastic shaft joints of the present invention constructed as described above, is as follows. Even in case of transmission of the rotational force, if the rotational force to be transmitted is of low torque, the rotational force is transmitted via the vibration absorbing member. When the rotational force to be transmitted is of low torque as described or when the rotational force is not transmitted, the vibration absorbing member prevents the transmission of the vibration between the coupling sleeve which is coupled and fixed to the rotary member, and the shaft. The vibration and displacement in the axial direction is absorbed when the vibration absorbing member is displaced in the axial direction or the vibration absorbing member and the shaft slide each other.
Also, when the torque of the rotational force to be transmitted is large, the pair of outer-diameter side engagement surfaces formed on one end of the shaft are brought into contact with the inner-diameter side engagement surfaces, and the rotational force is transmitted between the shaft and the rotary member to which the coupling sleeve is fixed. That is, the rotational force which can not be transmitted by the vibration absorbing member is transmitted by a contact portion between the outer-diameter side engagement surfaces and the inner-diameter side engagement surfaces. As a result, an excessive stress is not applied onto this vibration absorbing member, so that the durability of this vibration absorbing member can be sufficiently secured.
Since the rotary member and the coupling sleeve are coupled to each other by inserting the rotation limiting cylinder of this coupling sleeve between the pair of weight plate portions for forming this rotary member from the lateral opening thereof, this coupling work is not hindered even if there is a little gap between the axial position of the rotary member and that of the coupling sleeve. Also, it is not necessary to displace the shaft in the axial direction at the time of this coupling work. Consequently, there is no need to employ an expensive structure such as a serration engagement portion or the like.
If the shock absorbing member is provided, as stated in (1) above, it is possible to ease the impact which is applied to the body of the driver from the steering wheel at the time of crash accident, thereby protecting the driver more effectively.
Also, as stated in (2) above, if a rough engagement portion is arranged between the rotation limiting cylinder and the shaft, it is possible to prevent the shaft from falling off from this rotation limiting cylinder at the time of conveyance, thereby saving a trouble caused by the separation of the coupling sleeve from the shaft.
Also, as stated in (3) above, if the sealing members are arranged between the opening end portion of the retaining cylinder and the outer peripheral surface of the middle portion of the shaft, and at the opening end portion of the rotation limiting cylinder, it is possible to prevent foreign substances such as water or dust from advancing into the coupling sleeve, thereby preventing rust on the outer peripheral surface of one end portion of this shaft or increase of a sliding resistance of the sliding portion.
Further, as stated in (4) above, if, in the state in which the coupling sleeve is thrust into the interior part of the base portion of the rotary member, the coupling sleeve is arranged not to be drawn from the base portion owing to the engagement between the insertion plate and each of the locking portions, and moreover, the coupling sleeve is arranged to be urged upon the interior part of the base portion owing to the engagement between the outer peripheral surface of the middle portion of the coupling member and the elastic stretching piece, a work for coupling the shaft with the coupling sleeve mounted thereon to the rotary member can be conducted easily while making the center of rotation of one member corresponding to that of the other member.